1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus to be used when a mask pattern is transferred onto a substrate in the lithography step for producing devices including, for example, semiconductor elements, liquid crystal display elements, plasma display elements, and thin film magnetic heads. The present invention also relates to techniques in relation to the above.
2. Description of the Related Art
High exposure accuracy is required for the exposure apparatus of the full field exposure type (stepper type) or the scanning exposure type (for example, the step-and-scan system) to be used in order to produce semiconductor elements or the like. Therefore, the exposure apparatus adopts arrangements which make it possible to perform highly accurate positioning or highly accurate scanning for the reticle stage system for positioning the reticle as a mask and for the wafer stage system for two-dimensionally moving the wafer as a substrate respectively. The reticle stage system and the wafer stage system have been hitherto assembled successively and directly on a predetermined frame mechanism.
In order to further enhance the resolution, the recent exposure apparatus uses the exposure light beam of the ArF excimer laser (wavelength: 193 nm) having the wavelength shorter than that of the KrF excimer laser (wavelength: 248 nm). Further, it has been investigated to use, for example, the F2 laser beam (wavelength: 157 nm) having the shorter wavelength. However, the vacuum ultraviolet light (VUV light) as described above, which has the wavelength of not more than about 200 nm, has a high absorptance for ordinary air (especially oxygen). Therefore, when the vacuum ultraviolet light is used as the exposure light beam, it is necessary to adopt the following procedure. That is, respective stage systems are tightly enclosed in stage chambers (sub-chambers) respectively, and the gas such as nitrogen gas or helium gas, which has a high transmittance with respect to the vacuum ultraviolet light, is supplied into the stage chambers. Alternatively, the optical path of the exposure light beam at the inside of the stage chambers is substantially in vacuum. Such a procedure is also adopted in the same manner as described above for the space between adjacent lenses which are arranged at the inside of the projection optical system. Accordingly, it is necessary to adopt the following procedure for the exposure apparatus which uses the vacuum ultraviolet light as the exposure light beam. That is, the projection optical system is installed to the frame mechanism, and the respective stage systems are successively assembled. After that, the corresponding stage chambers are installed so as to surround the respective stage systems while maintaining the air-tightness.
The exposure apparatus, which uses, for example, the vacuum ultraviolet light as the exposure light beam as described above, is assembled by installing the stage chambers for maintaining the air-tightness after successively assembling the projection optical system and the respective stage systems with respect to the frame mechanism. However, the method, in which the respective stage systems, the stage chambers, and other components are successively assembled with respect to the single flame mechanism as described above, requires a considerable period of time to assemble and adjust the apparatus. Further, a long period of time is required, for example, to adjust the relative positions between the respective stage systems and the projection optical system. Therefore, an inconvenience arises such that the production cost of the exposure apparatus is increased. Further, the method, in which the respective stage systems, the respective stage chambers, and other components are successively assembled as described above, involves the following inconvenience as well. That is, the adjusting process is also complicated when the maintenance is performed for the exposure apparatus. As a result, the time and the cost required for the maintenance are increased.
Further, when it is intended to easily assemble and adjust the exposure apparatus with the arrangement in which the gas having a high transmittance with respect to the exposure light beam is supplied, for example, to the inside of the respective stage chambers, the following fear occurs. That is, the amount of leak of the gas having the high transmittance is increased, the concentration of the gas is decreased on the optical path of the exposure light beam, and the intensity of the exposure light beam is lowered on the substrate to be exposed therewith. When the gas having the high transmittance is an expensive gas such as helium gas, it is necessary to utilize the gas as effectively as possible in order to suppress the running cost.
Further, for example, when the helium gas is supplied to the optical path of the exposure light beam, the following fear also arises, because the refractive index differs relatively greatly between the helium gas and the atmospheric air (air). That is, if the contamination ratio of the atmospheric air changes on the optical path of the exposure light beam, the measurement accuracy of the laser interferometer for measuring the position of the stage system is lowered. Therefore, even when the assembling and the adjustment for the exposure apparatus are made easy, sufficient air-tightness is required for the optical path of the exposure light beam.
On the other hand, when the assembling and the adjustment for the exposure apparatus are made easy, it is also desirable that the respective stage systems and other components are miniaturized to be as small as possible in order to decrease the installation area (foot print) of the exposure apparatus.
Taking the foregoing problems into consideration, a first object of the present invention is to provide an exposure technique in which stage systems and other components are easily assembled and adjusted.
A second object of the present invention is to provide an exposure technique in which stage systems and other components are easily assembled and adjusted, and a gas, which transmits an exposure light beam, is supplied to at least a part of an optical path of the exposure light beam, wherein the gas is effectively utilized to make it possible to maintain a high concentration of the gas (maintain high air-tightness) on the optical path.
A third object of the present invention is to provide an exposure technique in which stage systems and other components are easily assembled and adjusted, the stage systems and other components can be miniaturized, and positions of movable sections and other components can be correctly measured.
Another object of the present invention is to provide a method for producing devices which makes it possible to produce a variety of devices at the low cost or at the high throughput by using such an exposure technique.